(a) Technical Field of the Invention
The present invention is related to a gearbox in all terrain vehicle power unit, and more particularly, to one that has a worm and an active lever mounted on the gearbox to transmit rpm of the transmission gear to a tachometer.
(b) Description of the Prior Art
Referring to FIG. 1 of the accompanying drawings, a belt transmission 2 in an automobile power unit of the prior art is accommodated in a gear box 11, and power generated from an engine 12 passes through a crankshaft 13 in a crankshaft case 15 to drive the belt transmission 2. The belt transmission 2 contains a slide disk 21 disposed on the crankshaft 13, a drive disk 22 provided on the crankshaft 13 and located to one side of the slide disk 21, an inclined plate 23 provided on the crankshaft 13 and located to the other side of the slide disk 21, a ball bearing 24 restricted in where between the slide disk 21 and the inclined plate 23, a passive shaft 25 linked to the belt transmission 2, two passive disks disposed on the passive shaft 25, a clutch 27 fixed to the passive shaft 25, a transmission belt 28 and a bearing 29 mounted on a cover 111 of the gearbox 11 to support the passive shaft 22. Wherein, the slide disk 21 and the drive disk 22 define an active disk for the belt transmission 2. One end of the transmission belt 28 is located at where between the driver disk 22 and the slide disk 21; and the other end, between those two passive disks 26.
Power generated from the explosion in the combustion chamber of an engine 12 pushes a piston 14 to engage in reciprocal movement to drive the crankshaft to rotate and both of the slide disk 21 and the drive disk 22 rotate synchronously; meanwhile, the ball bearing 24 travels when subject to eccentric force. As a throttle opens wider, the rpm of the crankshaft 13 increases to subject the ball bearing 24 to higher eccentric force; the ball bearing 24 starts to travel outwardly to hold against the slide disk 21; in turn, the slide disk 21 moves toward the driver disk 22 to narrow down the distance between the drive disk 22 and the slide disk 21, forcing the transmission belt 28 to expand for increased the coverage of the revolving circumference of the transmission belt 28 and further to increase the rpm of both passive disks 26 and accelerate the rear wheels (not illustrated) as driven by the gearbox 3 and the sprocket 37 with the power transmitted from the passive shaft 25 driven by the clutch 27. Consequently, the drive speed of the automobile is increased.
On the contrary, when the throttle is released, the eccentric force applied on the ball bearing 24 is reduced, and the distance between the drive disk 22 and the slide disk 21 gets larger in conjunction with the squeeze from the transmission belt 28 to reduce the coverage of the circumferential revolving of the transmission belt 28. Therefore, the drive speed of the automobile is decreased since the rpm of both passive disks is slowed down and that transmitted to the rear wheels is also slowed down due to the reduced rpm of the passive shaft.
Now referring to FIG. 2, the gearbox for the power unit to execute gear shifting function is comprised of a gearshift rod 31, a gearshift hub 32, a forked guide 33, a main shaft 34, an inverse link shaft 35 and a final shaft 36 provided in sequence in the gearbox 3. Wherein, a gear 311 of the gearshift rod 31 is mated to a gear 222 of the gearshift hub 32, one end of a gearshift fork 331 inserted to the forked guide 33 is inserted to a rail of position slot on the gearshift hub 321 while the other end of the gearshift fork 331 is inserted to a slide 341 of the main shaft 34. During the operation, the gearshift rod 31 is pushed to drive the gearshift hub 321 to revolve, thus to force one end of the gearshift fork 331 to travel in the rail of the position slot of the gearshift hub 321 to the position slot desired while the other end of the gearshift fork 331 drives the slide 341 to travel on the main shaft to engage the forward gear 342 or the backward gear 343 for completing the purpose of shift of position. Meanwhile, the power from the belt transmission 2 is transmitted through the passive shaft 25 to the final shaft 36 in the gearbox 3.
As illustrated in FIG. 1, the final shaft 36 in the gearbox 3 extends out of the gearbox 3 and a sprocket 37 is disposed at one end of the final shaft 36. A cover 38 provided over the sprocket 37 is adapted with a worm 391 and an active lever 392 linked to the gear rpm in the gearbox 3. Another end of the active lever 392 is connected to a grip of a tachometer wire 4. Once the final shaft 36 revolves, both of the worm 391 and the active lever 392 are driven to revolve. The driver reads the mileage and car speed from the tachometer on the instrument panel as driven by the wire 4. Though the prior art achieves its purpose of informing the driver about the mileage and car speed, the installation and transmission of the tachometer wire 4 requires parts including a screw 393, a sleeve 394, a bearing 395 and another screw 396. Both of the worm 391 and the active lever 392 are provided externally to the cover 38 of the sprocket resulting in greater horizontal width of the gearbox at the cost of the layout space for the entire body of the automobile. Furthermore, to provide service on the sprockets and chains, all the wire 4, the cover 38, the screw 396 and the sleeve 394 must be removed one by one.